Interchlamys mediacostata mediacostata (Hanna, 1926)
HANNA, G. D. 1926. Paleontology of Coyote Mountain, Imperial County, California. Proceedings of the California Academy of Sciences [4th Series], 14 (18): 427-503, text fig. 1, pls. 20-29. [p. 472, pl. 22, fig. 6; pl. 24, fig. 2]
1926 Pecten mediacostatus Hanna, 1926
G. D. Hanna, 1926, plates 22, 24.
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«Shell small, altitude a little greater than length, equilateral and equivalve, not noticeably inflated. Surface sculptured with 23 (in the type specimen) ribs which arc regularly rounded and are largest in the center of the valve. These ribs are strong at the ventral margin of the shell but are scarcely visible within 18 mm. of the beak; interspaces occupied by riblets, one to each, about one-third the size of the major ribs; in the better preserved specimens there is a fine even concentric sculpture of lirulae looped over the ribs, appearing as though cut with an engraving tool; anterior ear marked with five (in cotype) radiating riblets while the posterior (in the type) is smooth except for fine even concentric sculpture. Measurements of type specimen, a single right valve, altitude 37.2 mm.; length 30 mm. (slightly compressed longitudinally); thickness 8.5 mm.
Type: No. 1830, Ivlus. Calif. Acad. Sci. from Loc. 681 (C. A. S.) Alverson Canon on the south side of Coyote Mountain, Imperial County, California, in the Pliocene coral reef about midway up the canon. There is only one west coast species with which the sculpture of this can be compared, Pecten estrellanus (Conrad) of Miocene and lower Pliocene strata. That species is more inflated, longer than high, and the ribs extend entirely to the beak; moreover, the ribs are squarish and interspaces channeled on each side of the smaller riblet. Twenty-seven specimens were obtained from the coral reef of Alverson Canon, Loc. 681, and one from Loc. 683, both of the California Academy of Sciences' series. The reef is a wellmarked feature of the topography as onc ascends the canon. yet it does not appear to have been explored heretofore, since none of the numerous collections seen has contained this species. Like P. sancto-ludovici the specimens are more or less poorly preserved and usually somewhat crushed out of shape.» GEORGE DALLAS HANNA, 1926
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«RANGE: lower Pliocene, San Marcos and Imperial formations.
REMARKS: Two incomplete right valves were found at loc. A 3576. They have about 24 low rounded ribs with an intercalary in each interspace. Interspaces about half as wide as ribs. Posterior ear smooth above, faintly striated below. The hypotype is 47.2 mm high and 46.0 mm long (approximate). Hanna's specimens are compressed laterally so that the figures appear to have a much narrower apical angle. Pecten interlineatus aidei (Williston MS) Harris (Hodson, Hodson and Harris, 1927, p. 29, pI. 15, figs. 6, 9) from the Miocene of Venezuela is closely related but may be distinguished by the much heavier interribs in the interspaces.» DURHAM, J. W. 1950. Megascopic paleontology and marine stratigraphy. In 1940 E. W. Scripps Cruise to the Gulf of California, Part II. Geological Society of America Memoir 43: 1-216, pls. 1-48. [p. 65]
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Lyropecten mediacostatus (Hanna); J. W. Durham, 1950, Megascopic paleontology and marine stratigraphy, plate 7, figure 4.
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